Which of the following statements is true of Down's syndrome?

Correct Answer: D

Rationale: The correct answer is D. The likelihood of having a child with Down's syndrome increases as the age of the parents increases, particularly the mother's age. Choice A is incorrect because Down's syndrome is caused by an extra copy of chromosome 21, not a defect in the sex chromosomes. Choice B is incorrect as the symptoms of Down's syndrome and sickle-cell anemia are different. Choice C is also incorrect as Down's syndrome is not caused by a sexually transmitted infection during conception.

Correct Answer: D

Rationale: Matt is exhibiting symptoms typical of Huntington's disease (HD), a hereditary condition characterized by involuntary movements, cognitive impairment, and behavioral changes. The fact that Matt's father and grandfather had similar issues supports the genetic nature of the disease. Phenylketonuria (PKU) is a metabolic disorder that affects amino acid metabolism, not presenting with the symptoms described. Cystic fibrosis primarily affects the respiratory and digestive systems, not causing the neurological symptoms described. Turner syndrome is a genetic condition affecting females and is not associated with the symptoms described in the case of Matt.

Correct Answer: A

Rationale: The correct answer is A. Tay-Sachs disease is most commonly found among Jewish families of Eastern European descent. It is a fatal genetic disorder that affects the nervous system. Choice B is incorrect because Tay-Sachs disease does not involve excessive mucus production in the lungs and pancreas. Choice C is incorrect as it states that Tay-Sachs disease is most commonly found among Asian American families, which is inaccurate. Choice D is also incorrect because Tay-Sachs disease does not cause muscular dystrophy characterized by weakening of the muscles.

Correct Answer: B

Rationale: A sonogram, also known as an ultrasound, is a procedure that utilizes sound waves to generate images of a developing embryo or fetus. This imaging technique is commonly used in prenatal care to monitor fetal development and identify any potential abnormalities. Choices A, C, and D are incorrect because a phenotype refers to an individual's observable traits resulting from genetic and environmental influences, a genotype is an individual's genetic makeup, and an alpha-fetoprotein (AFP) assay is a blood test used to screen for certain birth defects.

Correct Answer: D

Rationale: The correct answer is D, Rubella. Rubella vaccine is recommended postpartum to prevent congenital rubella syndrome in future pregnancies. Pneumococcal and Hepatitis vaccines are not routinely given postpartum. Human papillomavirus vaccine is not typically administered immediately after birth but rather at a later age to prevent HPV infections.